To verify the Law of Malus for plane-polarized light with the help of photovoltaic cell.

 APPARATUS

Optical bench, halogen lamp, the double convex lens, polarizer, analyzer, photovoltaic cell and microammeter (0-50mA).

THEORY AND FORMULA  

According to Malus Law, when a beam of completely plane-polarized light is incident on the analyzer, then the intensity I of the emergent light is given by

                             I=I0​cos2φ    

Where I0 = Intensity of plane-polarized light incident on the analyzer.

               φ=angles between planes of transmission of the polarizer and the analyzer

To verify this law, light from the analyzer is made to enter a photovoltaic cell. The current output of the photovoltaic cell is connected to a microammeter.

 

PROCEDURE

1. In this arrangement, the convex lens source S., Polarizer P, Analyzer A, and the Photovoltaic cell window must be at the same height.

2. Now turn on the incandescent light. Light from source S rendered parallel with the help of a convex lens L is allowed to fall on polarizer P.

3. For each orientation of the polarizer P, the polarized light passes through analyzer A. The analyzer A is rotated until a maximum deflection occurs in the microammeter. The position of the analyzer is recorded on a circular scale. The corresponding micro-ammeter deflection was also recorded. The analyzer position corresponds to φ=0 (this is the angle between the transmission plane of the polarizer and the analyzer.)

4. Analyzer A is rotated through a small angle, say 10° and then a stable micro-ammeter deflection is recorded.

5. The experiment was repeated by rotating the analyzer through 10 degrees each time and noting the corresponding micro-amperemeter deflection until it was nearly zero.

OBSERVATION

S.No.	Angles through the analyser is rotated φ	Micro-ammeter reading		cos φ	cos2 φ	θ/cos2φ
		µA	θ
1.	10º
2.	20º
3.	30º
4.	40º
5.	50º
6.	60º
7.	70º
8.	80º

CALCULATION

Find the value of θ/cos2φ from each observation and plot the graph for cos2φ on X-Axis and θ on Y-Axis.

RESULT

The graph for cos2φ on X-Axis and θ on Y-Axis is a straight line and hence, Malus law is verified.

 PRECAUTIONS 

1. The position of the polarizer must not be disturbed during the experiment.

2. The light source, lens, polarizer, analyzer, and the solar cell must be height adjusted.

 SOURCES OF ERROR

1. The voltage applied to the light source must be constant throughout the experiment.

2. The experiment should be carried out in a dark room to avoid external light inside the photovoltaic cell.

3. Be careful when conducting the experiment as the bulb gets very hot.

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